Field
Implementations described herein generally relate to components and methods used in plasma processing of substrates, and more specifically relate to grooved surfaces for controlling RF return path lengths in plasma processing chambers and methods for forming the same.
Description of the Related Art
Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on substrates, such as organic light emitting diode (OLED) substrates and semiconductor substrates. PECVD is generally accomplished by introducing a precursor gas into a vacuum chamber having a substrate disposed on a substrate support. The precursor gas is typically directed through a gas distribution showerhead situated near the top of the vacuum chamber. The precursor gas in the vacuum chamber is excited into a plasma by applying a radio frequency (“RF”) power to a chamber electrode from one or more RF sources coupled to the chamber. The plasma forms a layer of material on a surface of a substrate that is positioned on a substrate support. The gas distribution showerhead is generally connected to an RF power source and the substrate support is typically connected to the chamber body to create an RF power return path.
The standard frequency of the RF generators mostly used in the industry is 13.56 MHz. However, lower and higher frequencies have been considered for plasma applications. For example, for PECVD applications, there is a trend to shift the RF frequency to values higher than 13.56 MHz, the preferred values being 27.12 MHz and 40.68 MHz (harmonics of 13.56 MHz). Higher frequencies allow for higher deposition rates in PECVD processes and thus increase productivity and lower production costs.
With large area plasma processing equipment, problems with plasma processing uniformity may arise when the RF frequency is higher than 13.56 MHz and a large size (large surface) substrate is used. The problem may be exacerbated when the largest dimension of the plasma reactor (the diagonal) is equal or larger than the free space wavelength of the RF electric power driving the plasma. Under such circumstances, the reactor size is no longer negligible relative to the free space wavelength of the RF electromagnetic wave. In such a case, the plasma intensity along the reactor is no longer uniform. Physically, the origin of such a limitation lies in the fact that the RF wave is distributed according to the beginning of a “standing wave” spatial oscillation within the reactor.
Thus, there is a need for components and methods for standing wave compensation that provide improved plasma processing uniformity.